Comprising a slab of semiconductor material

ABSTRACT

A slab of semiconductive material is positioned inside a rectangular waveguide transmission line to electrically change the phase shift within a waveguide. The slab is provided with two electrodes to which a D.C. bias signal is applied; the bias signal varies the conductivity of the semiconductor material to produce the desired phase shift by changing the effective dimensions of the waveguide.

United States Patent 11 1 Gray et al.

[ 51March 20, 1973 COMPRISING A SLAB OF SEMICONDUCTOR MATERIALInventors: Sidney Gray, Rockhill; Burton Joshua Levin, Cherry Hill;David Joseph Miller, Brigantine, all of NJ.

Assignee: RCA Corporation, New York, NY.

Filed: Aug. 6, 1971 Appl. No.: 169,692

us. 01. ..333/31 A, 317/234 R 1111.01. ..H01p 1/18 Field of Search..333/24 R, 24 o, 24.1, 31 A,

333/81 A; 332/51 w, 51 H, 52

[56] References Cited UNITED STATES PATENTS 3,048,797 8/1962 Linder..333/24 G UX 4/1961 Thomas ..333/81 8 X 11/1959 Gunn et al. ..333/81 BPrimary Examiner-Paul L. Gensler Attorney-Edward J. Norton [5 7 ABSTRACTA slab of semiconductive material is positioned inside a rectangularwaveguide transmission line to electrically change the phase shiftwithin a waveguide. The slab is provided with two electrodes to which aDC. bias signal is applied; the bias signal varies the conductivity ofthe semiconductor material to produce the desired phase shift bychanging the effective dimensions of the waveguide.

8 Claims, 4 Drawing Figures COMPRISING A SLAB OF SEMICONDUCTOR MATERIALBACKGROUND OF THE INVENTION This arrangement relates to an electricallyvariable waveguide phase shifter. Various techniques based on differenttheories of operation have been employed in the design and constructionof electrically variable waveguide phase shifters. The most common arenonreciprocal ferrite phase shifters and reciprocal diode phaseshifters. The operation of the non-reciprocal ferrite phase shifter isdependent upon the interaction between a slab of ferrite material and amagnetic biasing field for its phase shifting effect. However, therelatively high attenuation of microwave signals by ferrite material atmillimeter wavelengths has precluded this method of phase shifting inthis frequency range.

The diode phase shifters employ one or more diodes mounted inside awaveguide. The diodes are responsive to a D.C. bias voltage appliedacross the diode electrodes. The field produced by the bias voltageinduces a change in the electrical characteristics of the diode, whichin turn affects the microwave impedance at various points within thewaveguide. The change in impedance causes a change in phase shift in amicrowave signal transmitted through the waveguide. The position of thediode inside the waveguide is critical for proper phase shifterperformance; usually a combination of one or more strategicallypositioned diodes is needed to minimize the overall impedance mismatchat the input port of the phase shifter.

At millimeter wavelength frequencies, the internal dimensions of thewaveguide are relatively small so that accurate positioning of a diodeis a problem. Also, the attenuation of a microwave signal by a variablereactance diode increases with increasing frequency.

SUMMARY A section of rectangular waveguide transmission line and a slabof variable conductivity semiconductive material having two electrodesthereto, the slab having a thickness t, is used to provide a change ofphase shift for a microwave signal coupled to the waveguide. Thewaveguide has internal broad and narrow phase determining conductivewall dimensions, in a plane transverse to the direction of signalpropagation. The semiconductive slab is in contact with substantiallythe entire surface area of only one of the internal narrow dimensionedwaveguide walls. The microwave conductivity of the semiconductive slabis responsive to the polarity of a D.C. bias voltage applied across theslab electrodes. The polarity of the applied bias voltage changes theconductivity of the slab and causes the phase determining broad walldimension to electrically change.

In the drawings:

FIG. 1 is a cross section ofa PIN semiconductive slab structure.

FIG. 2 is a rectangular waveguide phase shifter using one PINsemiconductive slab of the type shown in FIG. 1.

FIG. 3 is a rectangular waveguide phase shifter using two PINsemiconductive slabs of the type shown in FIG. 1.

FIG. 4 is a rectangular waveguide phase shifter using two adjacent PINsemiconductive slabs of the type shown in FIG. 1.

DETAILED DESCRIPTION Referring to FIG. 1, there is shown a bulk PINsemiconductive slab, which is one type of variable conductivitysemiconductive device. The active semiconductor is a high resistivityp-type silicon material with boron and phosphorus diffused into each ofthe broad flat faces of the silicon material, to form p and n layersrespectively. The outer surfaces of the p and n layers are metallizedwith a contact film of a conductive material such as aluminum to formthe electrodes of the device. The conductivity of the PIN semiconductiveslab is responsive to the polarity of a D.C. bias voltage which may beapplied across the device electrodes. In its low conductivity state,when the polarity of the applied D.C. voltage is such as to reverse biasthe p-n junction between the high resistivity p-type silicon materialand the low resistivity n phosphorus diffused layer, a microwave signalwill penetrate the semiconductive material. In its high conductivitystate, when the polarity of the applied D.C. voltage is such as toforward bias the p-n junction, the penetration depth of thesemiconductive material for a microwave signal is relatively small.

Referring to FIG. 2, there is shown a rectangular waveguide phaseshifter internally dimensioned to operate in the dominant waveguidemode, TE The n side conductive electrode 10 of a PIN semiconductive slab11, which may be of the type shown in FIG. 1, is in electrical contactwith substantially the entire area of one of the narrow internalwaveguide walls having the dimension b. The p side electrode 12 of theslab 11 is parallel to and separated from the n side electrode 10 by anoverall slab thickness t. The p side conductive electrode 12 of the slab11 is in the form of a conductive comb-like pattern. The fingers of thecomb-like pattern are oriented in the direction of microwave propagationand therefore cause a minimal perturbation of microwave signals.

It is not critical for phase shifter performance that an electrode 10 or12 of the semiconductive slab 11 be in contact with the narrowdimensioned waveguide wall. The electrodes 10 and 12 may be located onwhichever surfaces of the semiconductive slab 11 most convenient forapplying a D.C. bias signal. In some structures it may be desirable toplace the electrodes on the front and rear or upper and lower edges ofthe slab, although such arrangements may require the provision ofapertures in the waveguide walls.

A D.C. bias voltage, from a source not shown, having a magnitude ofapproximately 50 volts has its negative terminal connected to one end ofa high inductance lead 13 and its positive terminal connected to thewaveguide and therefore to the electrode 10. The other end of the highinductance lead 13 is connected to the p side electrode 12 of the slab11. The (negative) bias voltage reverse biases the p-n junction withinthe slab 11 and therefore maintains the slab in its low conductivitystate so that the slab allows the transmission of microwave energy fromthe p side electrode 12 to the n side electrode 10 of the slab. Thus,under these bias conditions, the effective electrical internal broadwall dimension of the waveguide is a.

The reversal of the polarity of the D.C. bias voltage,

i.e., application of a bias voltage of approximately I volt to the pside terminal 12 of the slab 11 via the high inductance lead 13 which ispositive with respect to the waveguide (and therefore with respect tothe electrode 10) forward biases the p-n junction within the slab l1 andmaintains the slab in its high conductivity state so that the slabprevents the transmission of microwave energy from the p side electrode12 to the n side electrode 10 of the slab. Thus, under these new biasconditions the effective internal broad wall dimension of the waveguideis electrically reduced by the thickness, t, of the semiconductivestructure 11. The new internal broad wall dimension is a.

The phase shift, 4), of a microwave signal transmitted through a length,L, of rectangular waveguide is d) 2n'L/k where the waveguide wavelength,k,,, is

All: a l ll 14 The wavelength in free space, k is )t c/f where c 30 Xcm/sec and f is the frequency of operation in hz. The cutoff wavelength,A is dependent on the waveguide mode of operation and the internalwaveguide dimensions. The cutoff wavelength, A for the dominantwaveguide mode, TE in rectangular waveguide is X, 2a (4) where a is theinternal broad wall dimension of the waveguide.

A microwave signal transmitted through a length, L, of rectangularwaveguide transmission line is shifted in phase when the waveguidewavelength, A is changed. The waveguide wavelength, A of a microwavesignal propagating in the TE, mode is changed by electrically varyingthe internal broad wall dimension of the waveguide from a to a. Thechange in phase shift, Ad),

The change in phase shift, Ad), is independent of the direction ofpropagation of the microwave signal, so that the phase shifter hereindescribed is of the reciprocal type. Attenuation of the microwave signalpropagated through the phase shifter is minimized by positioning thesemiconductive slab 11 in a region of minimum electric field, i.e., inthe vicinity of the internal waveguide side wall b.

Referring to FIG. 3, there is shown a rectangular waveguide phaseshifter having a first semiconductive slab 21 of similar construction tothe slab 11, and with its p electrode in electrical contact with anarrow internal waveguide wall of height b. The p electrode 22 of asecond semiconductive slab 23, of similar con struction to the slab 11,is in electrical contact with the opposite narrow internal waveguidewall, also of height b. The semiconductive slabs 21 and 23 each havesecond parallel comb-like conductive electrodes 26 and 27 parallel tothe first electrodes 20 and 22, the electrodes 26 and 27 being connectedto the n regions of the slabs 21 and 23 respectively. Each of the slabs21 and 23 has a thickness, t, which separates the conductive terminals20, 27 and 22, 26.

The microwave conductivity of the semiconductive slabs 21 and 23 isdependent upon the polarity of a D.C. voltage from a bias source appliedto the second terminals 26 and 27 via a pair of high inductance leads24, 25, the other terminal of the bias source being connected to thewaveguide, and therefore to the n electrodes 26 and 27. A forward biasvoltage of approximately 1 volt applied across the electrodes of each ofi the semiconductive slabs 21 and 23 electrically reduces the internalbroad wall dimension of the waveguide from a to a 2:.

The internal broad wall dimension is a controlling factor in thedetermination of the relative phase shift of a microwave signaltransmitted through a rectangular waveguide supporting the TE mode (seeEquations 1, 2 and 4). A reverse bias voltage of approximately 50 voltsapplied across the electrodes of each of the semiconductive slabs 21 and23 causes the semiconductive slabs 21 and 23 to revert to their lowconductivity state and allow microwave propagation in the full internalwidth, a, of the rectangular waveguide. The semiconductor slabs 21 and23 are reverse biased by a bias source, not shown, when the positiveterminal of the bias source, is coupled to the n electrodes 26 and 27 ofthe slabs 21 and 23 via the high inductance leads 24 and 25 and thenegative terminal of the bias source is coupled to the p electrodes 20and 22 of the slabs 21 and 23 via the waveguide. The semiconductor slabs21 and 23 are forward biased by a bias source, not shown, when thepositive terminal of the bias source is coupled to the p electrodes 20and 22 of the slabs 21 and 23 via the waveguide and the negativeterminal of the bias source is coupled to the n electrodes 26 and 27 ofthe slabs 21 and 23 via the high inductance leads 24 and A differentphase shift change is obtained by applying a reverse bias voltage acrossthe electrodes of one of the semiconductive slabs and applying aforwardbias voltage of proper magnitude across the electrodes of theother semiconductive slab. The effect of such biasing is to electricallychange the internal broad wall dimension of the waveguide from a to a t.I

Referring to FIG. 4, there is shown a microwave phase shifter having aconterminous pair of semiconductive slabs 40 and 41 inside a rectangularwaveguide. The first semiconductive slab 40 has a surface in contactwith an internal waveguide wall having the dimension b. Thesemiconductive slabs 40 and 41 each have a thickness, t, and a heightsubstantially equal to the internal waveguide wall dimension b. Thesemiconductive slabs 40 and 41 may be of the type shown in FIG. 1. Thesemiconductive slabs 40 and 41 have first electrodes 42 and 43respectively in electrical contact with a common internal wall havingthe dimension a. The semiconductive slabs 40 and 41 also have secondelectrodes 44 and 45 respectively on opposite semiconductive surfacesthereof. The second electrodes 44 and 45 are electrically isolated fromeach other and the internal waveguide walls.

A D.C. bias voltage of the proper polarity causes an increase in thesemiconductive conductivity when it is applied across the electrodes ofeach semiconductive slab. The increase in semiconductive conductivityeffectively reduces the waveguide dimension a by an amount equal to thethickness, r, of the slab. Thus the bias voltage has the effect ofelectrically varying the critical phase determining waveguide dimension0.

A phase shift, (I), is obtained when the polarity of the applied biasvoltages is such that the first slab 40 is in its high conductivitystate and the second slab 41 is in its low conductivity state. Underthese bias conditions, the phase determining waveguide dimension ischanged from a to a t. A phase shift (1), is obtained when the polarityof the applied bias voltages is such that both slabs 40 and 41 are intheir high conductivity states. Under these bias conditions, the phasedetermining waveguide dimension is changed from a to a 2t.

What is claimed is:

1. An electrically variable phase shifter, the phase shift of which maybe controlled by a variable polarity bias signal, comprising a waveguidehaving internal broad and narrow phase determining conductive walldimensions measured in a plane transverse to the direction ofelectromagnetic wave propagation, a slab of semiconductive materiallocated inside said waveguide and having oppositely disposed majorsurfaces and a predetermined thickness therebetween, said slab having afirst electrode on one semiconductive surface thereof and a secondelectrode on an opposite semiconductive surface thereof, said slabexhibiting relatively high electrical conductivity when said signal isof a given polarity and a relatively low electrical conductivity whensaid signal is of opposite polarity, one major surface of said slabbeing parallel to and touching the surface area of one of said internalnarrow dimensioned waveguide walls, and means for applying said biassignal between said electrodes, whereby change of the polarity of saidapplied bias signal changes the electrical conductivity of said slab andthereby changes the effective value of said broad wall dimension.

2. A phase shifter according to claim 1, wherein one of said electrodesis parallel to and in electrical contact with said one narrowdimensioned internal waveguide wall.

3. A phase shifter according to claim 1, including a second slab ofsemiconductive material located inside said waveguide and having a giventhickness and first and second electrodes thereto, said secondsemiconductive slab being responsive to the polarity of an electric biassignal applied to the electrodes thereof, one major surface of saidsecond semiconductive slab being parallel to and touching the surfacearea of the narrow dimensioned waveguide wall opposite said one narrowdimensioned waveguide wall, whereby the polarity of the bias signalapplied to the first and second electrodes of said second slab changesthe conductivity of said second slab and thereby changes said internalbroad wall dimension.

4. A phase shifter according to claim 1, wherein said first electrode isin the form of a conductive comb-like pattern on the majorsemiconductive surface remote from said waveguide walls, said comb-likepattern having conductive fingers oriented in the direction ofelectromagnetic wave propagation.

5. A phase shifter according to claim 1, wherein said semiconductiveslab comprises a p region separated from an n region by a layer of highresistivity material, said p and n regions having conductive electrodesthereon.

6. An electrically variable phase shifter, the phase shift of which maybe controlled by a variable polarity bias signal, comprising a waveguidehaving internal broad and narrow phase determinin conductive walldimensions measured in a plane ransverse to the direction ofelectromagnetic wave propagation, first and second slabs ofsemiconductive material located inside said waveguide and each havingoppositely disposed major surfaces and a predetermined thickness, saidslabs each having a first electrode on one semiconductive surfacethereof and a second electrode on an opposite semiconductive surfacethereof, each slab exhibiting relatively high electrical conductivitywhen said signal is of a given polarity and a relatively low electricalconductivity when said signal is of opposite polarity, one major surfaceof said first slab being parallel to and touching the surface area ofone of said internal narrow dimensioned waveguide walls, and means forapplying said bias signal between the electrodes of each slab, said biassignal applying means having a first condition wherein the bias signalapplied to each of said slabs is of said given polarity, and a secondcondition wherein the bias signal applied to said first slab is of saidgiven polarity and the bias signal applied to said second slab is ofsaid opposite polarity, whereby change of the polarity of said appliedbias signal changes the electrical conductivity of said first and secondslabs and thereby changes the effective value of said broad walldimension.

7. A phase shifter according to claim 6, wherein one major surface ofsaid second slab is parallel to and touching the internal narrowdimensioned waveguide wall opposite said one narrow dimensioned wall.

8. A phase shifter according to claim 6, wherein a first slab majorsurface opposite said one major surface is parallel to and touching amajor surface of said second slab.

1. An electrically variable phase shifter, the phase shift of which maybe controlled by a variable polarity bias signal, comprising a waveguidehaving internal broad and narrow phase determining conductive walldimensions measured in a plane transverse to the direction ofelectromagnetic wave propagation, a slab of semiconductive materiallocated inside said waveguide and having oppositely disposed majorsurfaces and a predetermined thickness therebetween, said slab having afirst electrode on one semiconductive surface thereof and a secondelectrode on an opposite semiconductive surface thereof, said slabexhibiting relatively high electrical conductivity when said signal isof a given polarity and a relatively low electrical conductivity whensaid signal is of opposite polarity, one major surface of said slabbeing parallel to and touching the surface area of one of said internalnarrow dimensioned waveguide walls, and means for applying said biassignal between said electrodes, wherebY change of the polarity of saidapplied bias signal changes the electrical conductivity of said slab andthereby changes the effective value of said broad wall dimension.
 2. Aphase shifter according to claim 1, wherein one of said electrodes isparallel to and in electrical contact with said one narrow dimensionedinternal waveguide wall.
 3. A phase shifter according to claim 1,including a second slab of semiconductive material located inside saidwaveguide and having a given thickness and first and second electrodesthereto, said second semiconductive slab being responsive to thepolarity of an electric bias signal applied to the electrodes thereof,one major surface of said second semiconductive slab being parallel toand touching the surface area of the narrow dimensioned waveguide wallopposite said one narrow dimensioned waveguide wall, whereby thepolarity of the bias signal applied to the first and second electrodesof said second slab changes the conductivity of said second slab andthereby changes said internal broad wall dimension.
 4. A phase shifteraccording to claim 1, wherein said first electrode is in the form of aconductive comb-like pattern on the major semiconductive surface remotefrom said waveguide walls, said comb-like pattern having conductivefingers oriented in the direction of electromagnetic wave propagation.5. A phase shifter according to claim 1, wherein said semiconductiveslab comprises a p region separated from an n region by a layer of highresistivity material, said p and n regions having conductive electrodesthereon.
 6. An electrically variable phase shifter, the phase shift ofwhich may be controlled by a variable polarity bias signal, comprising awaveguide having internal broad and narrow phase determining conductivewall dimensions measured in a plane transverse to the direction ofelectromagnetic wave propagation, first and second slabs ofsemiconductive material located inside said waveguide and each havingoppositely disposed major surfaces and a predetermined thickness, saidslabs each having a first electrode on one semiconductive surfacethereof and a second electrode on an opposite semiconductive surfacethereof, each slab exhibiting relatively high electrical conductivitywhen said signal is of a given polarity and a relatively low electricalconductivity when said signal is of opposite polarity, one major surfaceof said first slab being parallel to and touching the surface area ofone of said internal narrow dimensioned waveguide walls, and means forapplying said bias signal between the electrodes of each slab, said biassignal applying means having a first condition wherein the bias signalapplied to each of said slabs is of said given polarity, and a secondcondition wherein the bias signal applied to said first slab is of saidgiven polarity and the bias signal applied to said second slab is ofsaid opposite polarity, whereby change of the polarity of said appliedbias signal changes the electrical conductivity of said first and secondslabs and thereby changes the effective value of said broad walldimension.
 7. A phase shifter according to claim 6, wherein one majorsurface of said second slab is parallel to and touching the internalnarrow dimensioned waveguide wall opposite said one narrow dimensionedwall.
 8. A phase shifter according to claim 6, wherein a first slabmajor surface opposite said one major surface is parallel to andtouching a major surface of said second slab.